Nano-Scratch Response of Diamond-Like Carbon Film Deposited by Pulsed Direct Current Magnetron Sputtering

Nano-Scratch Response of Diamond-Like Carbon Film Deposited by Pulsed Direct Current Magnetron Sputtering

T. Koch (Institute of Materials Science and Technology, Vienna University of Technology, Austria), M. Lackner (Institute of Surface Technologies and Photonics, Joanneum Research Forschungsges m.b.H., Austria), A. Pauschitz (AC2T Research GmbH, Austria) and Manish Roy (Defence Metallurgical Research Laboratory, India)
DOI: 10.4018/IJSEIMS.2020070102

Abstract

Diamond-like carbon (DLC) films are known for thermal, chemical and mechanical properties. Hydrogen free and hydrogenated DLC films are deposited using pulsed direct current magnetron sputtering. The influence of sputtering conditions on the nano-scratch properties of these films is investigated. Raman spectra reveals that structural disorder in the a-C:H matrix decreases with increase in acetylene flow. Increased acetylene flow reduces frictions, residual stress and retains hardness. The friction responses of the deposited defects free ultra-smooth films are influenced by pull off forces at low load and by formation of carbonaceous layer at high load.
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Introduction

Several attractive properties (Zehnder & Patscheider, 2000; Dean & Chalamala, 1999; Robertson, 2002; Neuville & Mathews, 1997; Donnet, 1996) of diamond-like carbon (DLC) films make them useful for number of applications including magnetic hard disc, microelectromechanical (MEMS) systems, biomedical applications (Grill, 1999; Jiang, Lu, Bogy, Bhatia, & Miyamoto, 1995; Roy, Kavasnica, Schalko, Eisenmenger-Sittner, Vorlaufer & Pauschitz, 2005), etc. In all these cases, thin coatings with superior wear resistance and low friction coefficients are desirable and hence DLC proves to be the most suitable particularly for ambient condition application. Although several techniques (Dall’Asén, Verdier, Huck, Halac, & Reinoso, 2006; Kohzaki, Higuchi, Noda, & Uccida, 1992; Bootkul, Supsermpol, Saenphinit, Aramwit, & Intarasiri, 2014; Pauschitz, Schalko, Koch, Eisenmenger-Sittner, Kavasnica, & Roy, 2003; Ronkainen, Koskinen, Anttila, Holmburg, & Hirvinen, 1992) are available for depositing DLC films, ECR-MPCVD is a promising technique where deposition takes place at low substrate temperatures (Sarakinos, Braun, Zilkens, Mraz, Schneider, Zoubos, & Patsalas, 2012) as it forms superior quality plasma. However, sputtering is a more widely used deposition method because of its advantages such as: low cost of operation, simplicity and control of the process and film homogeneity. The properties of the films deposited by sputtering, can be changed by adjusting the processing conditions such as sputtering and reactive gas flow, deposition pressure, sputtering power etc. By pulsing the sputtering voltage, structural and mechanical properties of DLC films can be improved further. The film can be made denser and the sp3 binding content can be increased by Ar bombardment (Robertson, 2002; Alami, Sarakinos, Uslu, & Wuttig, 2009). Pulsed DC sputtering also helps in suppressing the arcs (Grill, 1997) that can be used to reduce defect density in the deposited films when target material for sputtering is porous graphite.

Grill (1997) and Donnet (1998) reported the friction properties of DLC film. The friction coefficient of hydrogenated diamond-like carbon (a-C:H) depends on the relative humidity. The friction coefficient measured at low humidity is found to depend on the carbon precursor (Erdemir, Eryilmaz, & Fenske, 2000). The friction coefficient also varies with the C/H-ratio in the film. The highest friction coefficient is obtained for the film deposited with acetylene (C2H2) as precursor. On the other hand, CH4 as a precursor tends to form polymeric a-C:H films that have limited wear resistance due to their soft nature (Chowdhury & Laugier, 2004).

The nanotribological properties of DLC films have been studied using a variety of methods. Several investigators have assessed the strength and adhesion of carbon films by means of nanoindentation (Hsiao, Bogy, & Bhatia, 1998; Fang & Chang, 2006; Longothetidis & Charitidies, 1999; Fan, Nose, Diao, & Yoshida, 2013) and nanoscratch testing (Li & Bhushan, 1998; Deng, Scarf, & Barnard, 1997; Mate, 1993) to measure nanohardness and scratch resistance respectively. Employing scanning probe microscopy friction and adhesion properties of a-C:H films were investigated by Mate (1993b) and Perry et al., (1995). With the help of atomic force microscopy (AFM), nanotribology of carbon-based films was reported by several investigators (Beake, Hassan, Rego, & Ahmed, 2000; Kavasnica, Schalko, Eisenmenger-Sittner, Bernardi, Vorlaufer, Pauschitz, & Roy, 2006; Bogus, Gebeshuber, Pauschitz, Roy, & Haubner, 2004; Tomala, Pauschitz, & Roy, 2013). Despite extensive work in this field, basic understanding and systematic study of the sputtering conditions on the tribological properties is far from being satisfactory.

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